Helical electric immersion heater



Mrch 20,1945. P. B 'LEVITT 2,371,696

HELICAL ELECTRIC IMMERSION HEATER Filed July r1'7, 1943 IOO O I 2 3 4 5 6 7 8 9 lO JNVENTOR. PERCY 5. LEVITT TEMPERATURE` DISTRIBUTION ALONG HEATER v4Patterned Mar. 20, 1945 HELICAL ELECTRIC MMERSION .HEATER Percy B. Levitt, Millburn, N. J., assigner to Cities Service Oil Company, New York, N. Y., a corporation of Pennsylvania Application July 17, 1943, Serial No. 495,171

' (ci. 21e-3s) 8 Claims.

This invention relates to improvements in helical electric immersion heaters used for the heating of motor oils in the crankeases of air- .craft and other motor vehicles used at extremely low temperatures.

Electric heaters have been used to considerable extent for heating such motor oils, and it has been the general practice to make such heaters by winding an electric resistance wire in a helix around a refactory core, the windings being uni'- formly spaced along the core'. However, one'of the difficulties encountered in the manufacture and use of such heaters was to obtain the desired wattage rating for the heater and at the same time provide a heater that would have a useful life of reasonable length. It was found that heaters with uniform windings gave such high temperature difference along the winding that very coarse wire had to be used to get a rea-A sonable life from the heater. On the. other hand, it was diiiicult with such coarse wire to get the required resistance out of the space available. It was further found that the use of fine wire, which would give the desired resistance, would also fail very quickly because of the high local temperatures developed Where the windings were uniformly spaced.

After considerable trouble with helical electric Y heaters, a heater winding was developed in which the heat input per increment of length matched the vheat dissipation along the heater. This resulted in a heater in which the windings of the resistance wire were arranged so that the spacing in the intermediate. section of the heater were considerably greater than at the ends of the heater, and one in which the high local temper-4 atures previously encountered were no obtained. It was also found that fine resistance wire could be used in the new heater ,Without approaching the failure temperature of the wire and that with this new heater one could obtain a much higher load than witha similar heater having uniformlyr spaced windings. .Also in the manufacture of the improved heater of the present invention, the construction of the heaters was greatly facilitated by providing a grooved core with the grooves spaced so as to give the particularly desired distribution along the length of the heater. The improved electric heater of the present invention has other features and advantages which have contributed to its successful use.v

The primary object of the invention is to provide an improved helical electric immersion heater in which the Wlndlns are so distributed as to match the dissipation characteristic and avoid the production of localized high temperatures.

A further object of the invention is to provide a helical electric immersion heater in which the windings are so distributed as to permit the use of resistance wire of smaller gauge than otherwise would be possible and still avoid reducing the overload capacity of the heater.

A further object of the invention is to provide animproved refractory core for helical electric immersion heaters which will greatly facilitate the winding of the resistance wire in a predetermined spaced relation.

The improved heater of the present invention will be described more in detail hereinafter in connection with the accompanying drawing forming a part of this application.

In the drawing:

Fig. l is a side view of a heater constructed in accordance with the features of the present invention with certain parts in section and other parts broken away.

Fig. 2 is a chart showing temperature curves of the improved heater of the present invention and a temperature curve obtained from a similar heater having uniformly spaced windings.

The improved heater of the present invention as shown in Fig. l of the drawing, comprises an outer metal casing or sheath I0 which preferably 3o is cylindrical, but may be of any desired uniform cross section, 'and constructed of some metal of relatively high conductivity, such as Duraluf min, aluminum, copper, brass, or other suitable v the resistance wire windings terminate in leads` metal or alloy. The outer surface of casing I0 may be plain or provided with radial or longitudinal fins, grooves or channels. The casing IIl encloses a cylindrical cast refractory core I2 which is preferably made of zircon and provided with parallel helical grooves I4 and I6 in which are laid a resistance heating wire I 8. The wire may be of chromium, nickel, chromium alloy, aluminum-cobalt-iron alloy or other suitable composition. The resistance wire I8 is a looped resistance in which two parallel strands of the wire beginning with the loop at the left hand of the core is laid in parallel, respectively, in the grooves I4 and I6. At the right hand of the core,

20 and 22 which extend through a neck .sec-

tion 24 which is provided with a shoulder and end thread, as shown, for mounting the heater.

The core I2 is of uniform section and preferably cast from a zircon mix, with the grooves Il and I6 arranged so that the heat input per increment of length matches the heat dissipation,

2 Y asrneee resulting in a spacing in the intermediate or midsection ofthe core for a, considerable' distance (about 1/2 its length) of approximately twice that at the current-supply end of the heater, with the spacing at the opposite end being nearly the same as that at the current-supply end but slightly wider, as shown in the example. It will be noted that the spaces between windings from either end toward the central section of the heater are gradually wider. The looped resistance wire with parallel windings is preferred but the heating unit may be made by spacing a singleresistance wire wound in a helical groovearound the outside of the core to give the desired heat input characteristic, the core preferably being hollow so thatla lead wire may extend from the left hand end of the core through the core and to the current inlet end at the right.

In the structure shown in Fig. 1, the resistance wire is looped through a hole connecting the ends of the grooves Il and I6 and then wound on the core by a special winding machine. Before the core and resistance wire thereon are inserted into the casing I0, the unit is coated with a Zircon wash made of 50% milled grain zircon, 50% natural grain zlrcon bonded with a mixture of 6% P205 and 2% of chromic acid. This coating is hardened onto the wire and the core by heating the unit to a temperature of about 600 F. in an oven. The resulting coated heating unit is centered in the casing l and packed therein with a marginal layer of iine zircon sand 26 which is a good dielectric. The fine zircon sand is firmly packed into vthe casing `around the heating unit by vibrating the casing as the s and is introduced. T he electric resistance heating unit is finally sealed in the casing with a plug or head 28 which may be screwed or otherwise fastened in the endl of the casing I0.

The full line curve in Fig. 2 labeled Distributed Winding is a substantially flat temperature curve made by taking the temperatures with thermoture for approximately the mid-point of the heater wire of the uniformly spaced windings was 5 between 1400* and 1500" F. (approx. `1450 FJ. Furthermore, the temperatures at the ends of that heater'went considerably below the corresponding temperatures for the heater of Fig, l.

While the present invention is particularly diso rected to electric immersion heaters having a, low diameter-to-length ratio, of Example 1 to 5, the

invention may be applied to heaters of substanj tially different ratio. It is to be further understood that the heaters need not necessarily 4be circular in cross-section, but may be of some other convenient or desirable shape. 'I'he prob- 'lems discussed, such as` the high local tempera-- tures in the heater wires, are particularly encountered in heaters having relatively short length compared to their width or diameter.

Having described the invention in its preferred l form, what is claimed as new is: v Y

1. In an electric immersion heater for heating 1 lubricating cils `in an ou container associated 75 high temperatures in the heme with an internal combustion engine, the heater including a metal casing of relatively short length compared to its width, an electric resistance heating unit inside said casing arranged so as to supply heat to the metal casing and to heat the saine to a substantially uniform temperature, an improved heating unit comprising a refractory core oflinsulating material having acircumferential helical groove of uniform diameter ex- R0 tendingA from end to end ofthe core, a resistance greater distances apart along the intermediate section of the c ore.

2. In an electric 'immersion heater having an elongated electric resistance heating element substantially surrounded by a tubular metal shell, an improved resistance heating` element comprising a core of refractory insulating material having a uniform cross-section, and a helical electric resistance wire wound thereon from end to end ofthe core, the windings being spaced, farther apart at the intermediate section of thecore than atthe ends and arranged so that the heat distribution along the heater will givel a substantially at temperature curve.

3. In an electric immersion heater having an elongated electric resistance heating unit substantially surrounded by a tubular'metal shell, an improved heating unit comprising a core of refractory insulating material on which is wound a fine electric resistance heating wire in which the windings are of substantially uniform length and are arranged so that the'spacings in the intermediate section of the heater are considerably greater than at the ends of the heater.

4. In an electric heater having a low lengtho to-diameter ratio, an improved resistance heating unit comprising a refractory core of insulating material having a ne helical resistance wire wound thereon and in which the resistance wire windings are of substantially uniform diameter and are arranged so that the spacings inthe intermediate section of the heater are considerably greater than at the ends of the heater and also so arranged that a relatively flat temperature curve would be produced by taking the tem- -peratures along the heater wire when in operation.

5. In an electric immersion heater having a low length-todiameter ratio, an improved core of refractory insulating material and of substantially uniform cross-section having a spiral groove in its external surface andextending substantially the full length of the core, the convolutions of the groove being relatively closely spaced at the ends of the core and relatively widely spaced along its intermediate section.

6. In an electric immersion heater having a low length-to-diameter Aratio and an elongated electric resistanceheating element substantially surrounded'by a tubular metal shell, an improved resistance heating elementcomprising a core of refractory insulating material having a uniform 79 of, the windings being spaced farther apart at the intermediate section of the core than at the ends and arranged so the heat distribution along the heater will givea `v`substantially ilat temperature curve. thereby avoiding localized 'L An electric heater comprising a core having aresistanceheatinwirewmxndthereoninthey resistancev wire with windings of substantially il uniform diameter in which localized high temperatures in the wire are avoided, comprising a helical resistance wire in which the windings are spaced farther apart along the intermediate section of the heater than at the ends thereof and arranged so that the heat input per increment of length matches the heat dissipation of the heater at a predetermined substantially uniform temperature.

PERCY B. LEV'ITI. 

